The protocol architecture for SCE has been studied by 3GPP (3rd Generation Partnership Project) as disclosed in NPLs 1 and 2.
Further, for example, NPL 3 discloses that U-Plane (User-Plane) traffic is transmitted through an MeNB (Master evolved Node B) and an SeNB (Second eNB) in parallel for the purpose of offloading the MeNB.
Furthermore, NPL 4 discloses that for U-Plane protocol architecture disclosed in NPL 3, support of separate ciphering at the MeNB and the SeNB is required.
Note that LTE (Long Term Evolution) security specification is disclosed in NPL 5, for example.